A cylinder lock comprises a central core and an outer casing or housing in which the core rotates. The housing is mounted in a suitable housing securing construction. A number of examples of prior art technology describe devices that are adapted to provide a removable or exchangeable cylinder lock core that provide the benefit of enabling such locks to be quickly re-keyed by relatively unskilled persons. Such re-keying may be required as a result of a possible deficiency in security or as the result of a lost key or the failure to return a key.
Patent publication U.S. Pat. No. 6,076,386 (Etchells et al) describes a lock which includes a removable core wherein a retaining element in the form of a ball is disposed in a concentrical groove formed on a core housing. One drawback with this solution resides in the deficiency of a code-related blocking mechanism for removal of the core.
A car lock that includes a removable core is described in U.S. Pat. No. 2,036,764, where the connection between the core and an adaptor that actuates the lock operating device has the form of a bayonet fitting which can be removed without requiring the use of a tool to this end. In order to use the lock, it is necessary to insert a long user key into engagement with a groove in the adaptor in order to be able to rotate not only the core but also the adaptor. Removal of the core from the adaptor is achieved with a short key with which the core is rotated in a specific direction through 90° relative to the adaptor.
Although this latter solution provides a simple construction, it has several drawbacks. Firstly, it relies on the strength mechanics of the key tip for rotation of the adaptor, which results in an unreliable operation. Secondly, this lock can be manipulated relatively easily.